Abstract

Nanophotonic wire waveguides play an important role for the realization of highly dense integrated photonic circuits. The miniaturization of optoelectronic devices and realization of ultra-small integrated circuits strongly demand compact waveguide branches. T-shaped versions of nanophotonic wires are the first stage of both power splitting and optical-interconnection systems based on guided-wave optics; however, the acute transitions at the waveguide junctions typically induce huge bending losses in terms of radiated modes. Both 2D and 3D finite-difference time-domain methods are employed to monitor the efficient light propagation. By introducing appropriate combinations of dielectric posts around the dielectric-waveguide junctions within the 4.096μm×4.096μmregion, we are able to reduce the bending losses dramatically and increase the transmission efficiency from low values of 18% in the absence of the dielectric posts to approximately 49% and 43% in 2D and 3D cases, respectively. These findings may lead to the implementation of such T-junctions in near-future high-density integrated photonics to deliver optical-clock signals via H-tree network.

Figures (11)

Schematic drawing of the T-junction nanophotonic wire dielectric waveguide is shown. The width and refractive index of the dielectric slab (w) is 0.20a and 3.46, respectively. The equally divided input light pulse is shown in the branches. The arrows indicate the direction of the signal flow.

The power transmission spectra of three cases are shown. A regular T-junction nanowire dielectric waveguide corresponds to solid-black line. The dashed-green line represents the transmission efficiency of the structure whose schematic drawing is presented in Fig. 4. The T-junction nanowire dielectric waveguide is surrounded by photonic crystal that is composed of dielectric rods with radii, r = 0.20a. The dotted-red line corresponds to the power transmission efficiency spectrum for the case in which r1and r2are adjusted to be 0.18a and 0.26a, respectively. The structure in this case is presented in Fig. 5.

Steady-state electric field (Ez) distribution of TM mode for the regular T-junction nanowire waveguide when the operating frequency is centered atλ=1.55μm. The red and blue colors represent the maximum and minimum electric-field values, respectively.

Schematic of T-junction nanowire dielectric waveguide surrounded by square-lattice photonic crystal that is composed of dielectric rods with radii, r = 0.20a. The box shows the boundary of the region that is engineered to enhance transmission efficiency. It covers an area of (8ax8a = 4.096μm×4.096μm).

Schematic drawing of the modified hybrid T-junction. In the first step, two additional cylinders represented by “A” are embedded along the diagonal direction. In the next attempt, the radii of the cylinder pointed with arrows are arranged in order to enhance the transmission of the light-wave. Finally, (δx, δy) describes the cylinders movement along the diagonal direction. δx and δy values are selected with the equal amount to stay on the diagonal direction.

Steady-state electric field (Ez) distribution of TM modes for the hybrid structure when the operating frequency is centered at a/λ = 0.33. The red and blue colors represent the positive and negative electric fields, respectively. The arrows indicate the propagation directions.